Papers by Keyword: Oxygen Precipitation

Abstract: The results of this work have shown that for microelectronic applications, gettering at dislocations is less important and oxygen precipitates are the main getter sink for Cu. Sufficient gettering of Cu in samples contaminated with low Cu concentration requires a higher density and larger oxygen precipitates compared to samples contaminated with high Cu concentration. It is demonstrated that the getter efficiency depends on the contamination level of the samples and getter test with low contamination level must be applied for microelectronic applications. Furthermore, a getter test for 3D chip stack technologies was developed. It was shown that although the wafers are thinned to a thickness of 50 μm their getter efficiency seems to be higher than for wafers of the original thickness. This is assumed to be due to the higher Cu concentration in the thinner wafers which can be gettered easier. It is also demonstrated that BMDs can getter Cu impurities even if the temperature does not exceed 300 °C. The getter efficiency tends to be higher if the samples are stored under day light and not in the dark.

Abstract: We report a strategy feasible for improving the internal gettering (IG) capability of iron (Fe) for n/n⁺ epitaxial silicon wafers using the heavily arsenic (As)-doped Czochralski (CZ) silicon wafers as the substrates. The n/n⁺ epitaxial silicon wafers were subjected to the two-step anneal of 650 °C/16 h + 1000 °C/16 h following the rapid thermal processing (RTP) at 1250 °C in argon (Ar) or nitrogen (N₂) atmosphere. It is found that the prior RTP in N₂ atmosphere exhibits much stronger enhancement effect on oxygen precipitation (OP) in the substrates than that in Ar atmosphere, thereby leading to a better IG capability of Fe contamination on the epitaxial wafer. In comparison with the RTP in Ar atmosphere, the one in N₂ atmosphere injects not only vacancies but also nitrogen atoms of high concentration into the heavily As-doped silicon substrate. The co-action of vacancy and nitrogen leads to the enhanced OP in the substrate and therefore the better IG capability for the n/n⁺ epitaxial silicon wafer.

Abstract: The effect of annealing temperature on oxygen precipitation was investigated in various dose fast neutron irradiated Czochralski silicon (CZ-Si). Fourier Transform Infrared Absorption Spectrometer (FTIR) was used to measure the concentration of interstitial oxygen ([O_i]). Bulk microdefects (BMDs) were observed by optical microscope. The behavior of oxygen precipitation depends on the annealing temperature and the concentration of irradiation-induced defects. The mount of oxygen precipitates of irradiated samples is more than that in non-irradiation samples and increases with increasing the irradiation dose. Because of the effect of temperature on critical radius r_c and the oxygen diffusivity, oxygen precipitation increase with the increase of temperature at the studied lower temperature range, while decrease with the increase of temperature at the studied higher temperature range. High density dislocation and stacking faults generate in irradiated sample.

Abstract: Electron irradiation on silicon results in the creation of vacancy (V) and silicon self-interstitial (I).Vacancy tends to integrate with oxygen and forms the complexes of vacancy and oxygen (V_mO_n) such as VO, VO₂, and VO₃. These complexes of vacancy and oxygen in silicon have been the subject of extended investigations by standard methods such as infrared absorption. In infrared spectrum, the different V_mO_n has the corresponding peak. Irradiation induced defects as the core of oxygen precipitate can accelerate the oxygen precipitation. Oxygen precipitation plays an important role in the internal gettering (IG). In electron irradiated silicon, annealing at 300700 °C leads to the formation of two types of electrically active centers that are shallow thermal acceptors (TAs) and the well-known thermal donors (TDs). In this paper, the generation conditions, the infrared peaks of V_mO_n, the types of oxygen precipitation induced defects, the characters of TAs and TDs are studied.

Abstract: In order to investigate the performance of silicon single crystal depended on the annealing temperature, the minority carrier lifetime, the resistivity and oxygen concentration after different temperature annealing in Ar ambient were examined. And the effect of oxygen and related defects formed during annealed on the minority carrier lifetime were analyzed by microwave photoconductivity method, Fourier transform infrared spectrometer and four-probe measurement. The results indicate that after 450°C annealing for 30h, the resistivity and minority carrier lifetime of silicon increase significantly, while the concentration of interstitial oxygen decreases. After the annealing at 650°C, oxygen donor can be removed and the resistivity and the minority carrier lifetime decrease. During the high-temperature (above 650°C) annealing, the oxygen precipitation can decrease the minority carrier lifetime silicon.

Abstract: Oxygen precipitation (OP) and annihilation of voids in heavily phosphorus (P)-doped Czochralski (Cz) silicon have been investigated. It was found that the nucleation anneal at 650°C resulted in much more pronounced OP in the subsequent high temperature anneal than that at 800 or 900 °C. This was due to that SiP precipitates could be formed in heavily P-doped Cz silicon by the 650oC anneal and they acted as the heterogeneous nuclei for OP in the following anneal at high temperatures. The rapid thermal anneal (RTA) at 1200°C was proved to be an effective means to annihilate voids. Moreover, it was found that the significant OP resulting from the two-step anneal of 650°C/8 h + 1000°C/16 h could also cause the substantial annihilation of voids in heavily P-doped Cz silicon. The mechanisms for the annihilation of voids have been tentatively discussed.

Abstract: Oxygen precipitation (OP) behaviors were investigated for Czochralski (Cz) silicon wafers, which were coated with silicon nitride (SiNx) films or not, subjected to two-step anneal of 800C/4 h+1000°C/16 h following rapid thermal processing (RTP) at different temperatures ranging from 1150 to 1250C for 50 s. It was found that OP in the Cz silicon wafers coated with SiNx films was stronger in each case. This was because that nitrogen atoms diffused into bulk of Cz silicon wafer from the surface coated SiNx film during the high temperature RTP. Furthermore, it was proved that the RTP lamp irradiation facilitated the in-diffusion of nitrogen atoms, which was most likely due to that the ultraviolet light enhanced the breakage of silicon-nitrogen bonds.

Abstract: Oxygen precipitation in silicon has been studied in-situ by high energy X-ray diffraction. A gain of diffracted intensity is expected if an ideal crystal is distorted by growing precipitates as the diffraction mode changes from a dynamical to a more kinematical one. Irreversible changes in the intensity of a 220 and a 400 Bragg peak are detected for Czochralski grown samples only, but not in a float zone grown reference crystal. Thus, these changes are attributed to oxygen precipitation, which is confirmed by a subsequent classical ex-situ characterization. Further, the changes of the intensities of the two measured Bragg peaks are compared to each other to get the level of change in the diffraction mode from a dynamical to a kinematical one. The detection limit of the specific setup is estimated via a simulation of the defect inventory to correspond to a precipitate diameter of 50nm with the density of 6.9•109 1/cm3. The diffraction experiments are done with polychromatic and divergent X-rays generated by a laboratory source, albeit with high energy. This results in a simple and accessible setup for the characterization of oxygen precipitates.

Abstract: Low temperature boron and phosphorous diffusion gettering (BDG and PDG) of iron in Czochralski-grown silicon were experimentally studied. Differences and similarities between the gettering techniques were clarified by using intentionally iron contaminated wafers emphasizing especially the effect of oxygen. Experiments showed that the surprisingly high gettering effects of BDG could be explained by B-Si precipitates. Oxygen precipitation was seen to decrease minority carrier diffusion length after long gettering at low temperatures in both BDG and PDG. In the case of BDG oxygen precipitation affected more as a higher thermal budget was needed to obtain similar sheet resistance to that of PDG. According to experiments the efficiency of BDG can not be concluded from the sheet resistance, whereas the efficiency of PDG can. This has practical influences in a process control environment.

Abstract: In this paper, the influence of the rapid thermal annealing of single crystalline Cz-Si wafers on the evolution of the concentration of interstitial oxygen as well as oxygen in precipitated oxide phase was investigated by infrared spectroscopy. The wafers were preliminary furnace annealed to create the precipitate seeds. The concentration of interstitial oxygen was shows to decrease considerably as a result of annealing during up to 40 min together with the growth of the concentration of precipitated oxygen. This effect depended on the purity and defect structure of initial wafers. The kinetic model was developed to account for the observed effects based on the modification of the solubility level for interstitial oxygen induced by defects as well as its diffusivity. Obtained results of simulation agree well with the experimental data.